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Plane through a Point and containing a Line:


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Find the equation of the plane, P, through A(-3, 4, -1) containing the line L: x = 2 - t, y = -3 + 2t, z = 1 + 4t. See the diagram.

We can use two values of t, say t = 0 and t = 1, to find points B and C on the line. Then we can use the given point A to obtain the vectors AB and AC, which will lie in the desired plane, P. By forming the cross product, AB ´ AC, we obtain a vector perpendicular to each of AB and AC. This last vector can be used as the normal vector, n, to describe the plane.

First, find the point B, associated with t = 0:

xB = 2 + 0, yB = -3 + 0, zB = 1 + 0.

Hence, we have B(2, -3, 1).

Next, find C using t = 1:

xC = 2 - 1 = 1, yC = -3 + 2*1 = -1, zC = 1 + 4*1 = 5

Hence, we have C(1, -1, 5).

Now determine the two vectors in the plane:

AB = [xB - xA]i + [yB - yA]j + [zB - zA]k

= [2 - (-3)]i + [(-3) - 4]j + [1 - (-1)]k = 5i - 7j + 2k

AC = [xC - xA]i + [yC - yA]j + [zC - zA]k

= [1 - (-3)]i + [(-1) - 4]j + [5 - (-1)]k = 4i - 5j + 6k

Next determine the normal vector from the cross product:

, or

Finally, we use the normal, n, and the point A in the scalar equation of the plane:

a*[x - xA] + b*[y - yA] + c*[z - zA] = -32*[x - (-3)] -22*[y - 4] + 3*[z - (-1)] = 0.

Simplifying, we get

-32x - 22y +3z = 5.

As a check on our work, we can substitute each of the three points into this equation to make sure that they satisfy it:

A(-3, 4, -1): -32*(-3) - 22*4 + 3*(-1) =5

B(2, -3, 1): -32*2 - 22*(-3) + 3*(-1) = 5

C(1, -1, 5): -32*1 - 22*(-1) + 3*(-1) = 5


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General Contents

Detailed Contents

Index